Complex dielectric functions for graphene and hBN are displayed in Fig. REF  (a) and Fig. REF  (b), respectively. These ab-initio calculations use the time-dependent density functional
theory in the local density approximation (LDA), and are implemented in the Python code GPAW, a real-space electronic structure code using the projector augmented wave method. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.\(^{,}\)  [1]}, [2]}, [3]}, [4]} Both graphene and hBN dielectric functions are calculated in the armchair configuration for a momentum transfer value of \(0.05\,\) Å\(^{-1}\) , along the \(\bar{\Gamma }\) -\(\bar{M}\)  direction of the surface Brillouin zone. The armchair configuration and value of \(k\)  are selected for comparison of EELS with existing data in the literature obtained via density functional theory (DFT) methods. The \(k\) -point sampling with \(30 \times 30 \times 1\)  Monkhorst–Pack grid was chosen for the band-structure and EELS calculations for both graphene and hBN.
